Burj-Al-Arab

Small Boring Unit (SBU)

Conquering the Hard Rock Under Big Sky in Record Time

• Machine Type: Small Boring Unit (SBU)
• Diameter: 30 in (760 mm)
• Tunnel Type: Water Pipeline
• Tunnel Length: 216 ft (66 m)
• Owner: The Yellowstone Club
• Contractor: Tunnel Systems Inc.
• Location: Big Sky, Montana, USA

Project Overview

The Yellowstone Club, a private resort in Big Sky Montana, includes an 18-hole championship mountain golf course in addition to miles of ski trails. This golf course is irrigated by 318 ft (96.9 m) of pipeline from a nearby 79 million gallon reservoir.

In 2005, the project owner contracted Tunnel Systems Inc. to bore the pipeline. The contractor started out with an Auger Boring Machine with a �Christmas tree' head attachment. However, they ran into problems 59 feet (18 m) into the dig when they began boring through hard rock. The next two days of the bore cleared only 16 feet (4.9 m). For the rest of the dig, Tunnel Systems Inc. leased a Robbins 30 in (762 mm) diameter Small Boring Unit (SBU).

Geology

The section of pipeline through hard rock contained mixed ground conditions including sections of solid rock and mixed rock with soil.

SBU

Tunnel Systems elected to utilize a Robbins SBU because they are designed for bores just like this project -- in rock with an Unconfined Compressive Strength (UCS) greater than 24,000 kPa (3.5 ksi). They utilized an SBU without stabilizer feet, available on 30 in (762 mm) and 24 in (609 mm) models. Stabilizer feet are standard on all SBU models 36 in (914 mm) in diameter and above, as well as available on some 30 in (762 mm) models. The SBU featured Robbins' patented disc cutters to obtain the highest advance rates in hard rock. The SBU's design is based on the same technology as the large-diameter tunnel boring machines.

Tunnel Excavation

At the jobsite, the SBU was welded to the lead pipe casing. In order for the boring to begin, the SBU received thrust from the pipe casing and torque from the Auger Boring Machine (ABM). Muck was then removed through the auger.

Upon restarting the dig, the SBU achieved impressive advance rates of 43-49 ft (13.1-14.9 m) per day. The ABM and SBU bored through solid rock for approximately 197 ft (60 m) and bored through mixed rock and soil for the final 20 ft (6 m).

The SBU finished the project on time despite some setbacks. Harsh weather conditions on the job site of 19 degrees Fahrenheit (-7 degrees Celsius) and 40 mph (65 km/h) winds made it too difficult to work and the bore was forced to halt until the snowstorm passed. The crew completed the project in just a few hours on the following day.

Double Shield TBMs

For projects with difficult ground that still demand the speed of a Main Beam TBM

Fractured rock can be an insurmountable obstacle if you buy the wrong machine. Your crew safety and efficiency is at risk, and so is your schedule. With a Robbins Double Shield Tunnel Boring Machine (TBM), your project can have a great safety record and peak performance.

Robbins is no stranger to this type of TBM design. In fact, this is another type of TBM we invented! In 1972 Robbins built the world's first Double Shield TBM for a customer who anticipated tunneling through large sections of fractured rock. In recent years, several Robbins Double Shield TBMs have broken world records for production.

What is a Double Shield?

A Double Shield TBM consists of a rotating cutterhead mounted to the cutterhead support, followed by three shields: a telescopic shield (a smaller diameter inner shield which slides within the larger outer shield), a gripper shield and a tail shield.

In normal operation ("double shield mode"), the gripper shoes are energized, pushing against the tunnel walls to react the boring forces. The main propel cylinders are then extended to push the cutterhead support and cutterhead forward. The rotating cutterhead cuts the rock. The telescopic shield extends as the machine advances keeping everything in the machine under cover and protected from the ground surrounding it.

The gripper shield remains stationary during boring. A segment erector is fixed to the gripper shield allowing pre-cast concrete tunnel lining segments to be erected while the machine is boring. The segments are erected within the safety of the tail shield. It is the Double Shield's ability to erect the tunnel lining simultaneously with boring that allows it to achieve such high performance rates. The completely enclosed shielded design provides the safe working environment.

If the ground becomes too weak to support the gripper shoe pressure, the machine thrust must be reacted another way. In this situation, the machine can be operated in "single shield mode". Auxiliary thrust cylinders are located in the gripper shield. In single shield mode they transfer the thrust from the gripper shield to the tunnel lining. Since the thrust is transferred to the tunnel lining, it is not possible to erect the lining simultaneously with boring. In the single shield mode, tunnel boring and tunnel lining erection are sequential operations.

Regardless of the operating mode, working crews remain protected within the shields. Robbins Double Shield TBMs are capable of safely excavating a wide range of geologic conditions on a project. Our Double Shield TBMs are manufactured to suit your project requirements, in diameters from 1.6 m to 15 m (5 to 50 ft).

Double Shield TBM Features

Standard Features on all Robbins Double Shield TBMs:

• Flat, low profile cutterhead to enhance face support in broken rock.
• Recessed muck bucket openings with grill bars to prevent ingestion of large rock blocks.
• Back-loading cutters for safe cutter changing in unstable rock conditions.
• Dual thrust-reaction systems, enabling thrust reaction from the tunnel walls or the tunnel lining.
• High-speed segment erector (single- or dual-arm depending on machine diameter) installs pre-cast concrete segments with precision.
• Two-piece articulated telescopic shield offers safety, access to surrounding ground for examination and treatment, and smooth steering through curves.
• Digital guidance system for continuous information on alignment for maintaining strict control of tunnel line and grade.

Optional Features available on Robbins Double Shield TBMs:

• Closeable muck bucket doors
• Tail seals and greasing system
• Ultra high emergency thrust system

Robbins Double Shield TBMs can be customized with:

• Probe drills for pre-excavation investigation and ground consolidation
• Variable cutterhead speed
• Methane and other gas detectors
• Data acquisition system: Automatic acquisition, monitoring and storage of real-time data from the machine functions including penetration rate, thrust pressure, cutterhead speed, gripper pressure and many more machine parameters.
• Automated, precision guidance system, including ring-build option for shielded TBMs
• Guidance data acquisition system
• Closed circuit television systems
• Automatic fire suppression systems
• Closed loop cooling systems for conservation of water

Robbins designs Double Shield TBMs to meet the criteria of each specific project, including the geologic conditions, tunnel design, construction plan, project schedule, site logistics and many other factors. When you contact Robbins, we review your project specifications to determine the best tunneling system for your project. In some cases, an entirely new tunnel boring machine will be the answer and on other projects, the best decision may be to refurbish an existing TBM, to save you time and cost.

To learn more about Robbins' past projects, search our Project Solutions section. This section will give you an idea of what history-making successes we have accomplished in the past and how our innovative solutions can make your next project a success.

Whether you are in the planning phase of tunnel construction or about to bid on a project, our engineers and sales engineers can help you identify the best solution to achieve your objectives. For more information, complete our on-line inquiry form or contact The Robbins Company at your nearest location.

Double Shield TBM

Small-diameter Double Shield TBM helps clean up Cleveland

• Machine Type: Double Shield TBM
• Diameter: 2.2 m (7.2 ft)
• Tunnel Type: Waste Water
• Tunnel Length: 2.62 km (1.63 mi)
• Owner: Northeast Ohio Regional Sewer District
• Contractor: Marra/Majestic JV
• Location: Cleveland, Ohio

Project Overview

The Cleveland Heights Interceptor Project is a sewer system improvement project located in the Heights/Hilltop area of Cleveland. The project is one of hundreds projects mandated by the USA Environmental Protection Agency in the wake of the Clean Water Act which required communities to improved the quality of America's river and lake water. (For more information on the Clean Water Act and its effects, see http://www.epa.gov/r5water/cwa.htm).

During the torrential rains of spring and summer in the Cleveland area, the water flow overcame the existing sewer system resulting in flooding and the discharge of untreated water into Lake Erie. Larger-diameter pipelines were proposed to help reduce the basement flooding and sewage overflow problems which were common in the crowded urban area.

Geology

The TBM passed mostly through gray Berea sandstone that is fine to medium grained and significantly fractured in discrete zones. The rock has moderate to high abrasiveness as well as a potential for gas and water inflows from fissures and joints.

TBM and Back-Up

Robbins designed the 2.2 m (7.2 ft) diameter TBM to bore through fractured rock with potentials for water inflow. The TBM included a variable speed, hydraulic cutterhead drive and a high-capacity asymmetric main bearing. The machine also included roof and probe drills for rock support and pre-excavation ground investigations respectively. The TBM featured 12 inch (305 mm) cutters that could generate a maximum thrust of 4,472 kN (1,006,000 lb). Maximum cutterhead torque was 194,172 N-m (146,000 lb-ft). The 60-ton, gantry-style back-up system was designed to run efficiently with muck cars at maximum capacity.

Tunnel Excavation

The TBM began boring in July 1998. It experienced few problems and achieved impressive daily advance rates. Between the months of September and December 1998 the machine averaged 42 m (138 ft) per day and achieved a best day of 55 m (182 ft) bored. The machine finished in December 1998 with a monthly average of 442 m (1450 ft). Crews worked in 5-day work weeks with 2 shifts per day and the machine averaged 21 m (69 ft) per shift.

Small Boring Unit (SBU)

Robbins SBU bores through hard rock in just 8 working days

• Machine Type: Small Boring Unit (SBU)
• Diameter: 66 in (1.67 m)
• Tunnel Type: Water Pipeline
• Tunnel Length: 118 ft (36 m)
• Owner: Charlotte-Mecklenburg Utilities (CMU)
• Contractor: Horizontal Unlimited Inc.
• Location: Pineville, North Carolina, USA

Project Overview

This project, owned by Charlotte-Mecklenburg Utilities (CMU), required the installation of 15 miles (24 km) of pipeline south of Charlotte. The pipeline ranges from 36 inches (914 mm) to 64 inches (1.62 m) in diameter and increases the volume of water to meet higher consumer demands in the area.

Horizontal Unlimited Inc. was contracted specifically for a short 118 ft (36 m) section of pipeline through hard rock. In 2001, Horizontal Unlimited Inc. bought a Robbins 66 in (1.67 m) diameter Small Boring Unit (SBU) for the section of tunnel.

Geology

The portion of pipeline runs through hard gabbro. Gabbro is a plutonic igneous rock that is densely grained and mica rich. Drill and blast was not an option because the section of rock was free of fissures and would not fracture.

SBU Features

Robbins built the 66 inch (1.67 m) diameter SBU, the first manufactured of that diameter, to bore through very hard rock. Robbins SBUs utilize hard rock TBM disc cutter technology adapted for small-bore applications. Each unit includes a rugged cutterhead, high thrust/torque bearing assembly, front shield with stabilizer feet, and standard auger adaptation.

Tunnel Excavation

Workers aimed the SBU at a 5% grade because of close proximity to apartment buildings. Horizontal Unlimited used 5.5 ft (1.67 m) diameter snap-together pipe to minimize welding time. The SBU bored straight and ended up only 1.0 inch (25 mm) high of the target. The entire bore took just eight working days.

Earth Pressure Balance Machine

The USA's first-ever Hybrid EPB Shield Machine bores through Florida limestone

• Machine Type: Earth Pressure Balance Machine
  

• Diameter: 2 x 10.0 m (32.8 ft)
• Tunnel Type: Waste Water
• Tunnel Length: 2.8 km (1.8 mi)
• Owner: Tampa Bay Water
• Contractor: Kenko Inc.
• Location: Tampa, Florida, USA

Project Overview

The South Central Hillsborough Intertie tunnel passes under the Alafia River in Tampa Bay. The tunnel is part of Master Water Plan Stage B, an ambitious three-stage plan to replenish Florida's depleted groundwater.

Tampa Bay Water, the project owner, awarded Contract 2 for the South Central Intertie to Kenko Inc. in 2002. The contractor chose an innovative new solution to deal with the difficult ground conditions of the tunnel�a Robbins hybrid EPB shield machine.

Geology

The tunnel travels though the extremely permeable, highly fractured limestone of the Floridian aquifer with over 2.5 bar of hydraulic face pressure. Above the limestone is a layer of very stiff green clay and above the clay is a 4.6 m (15 ft) thick layer of loose, silty fine sand.

EPBM

The contractor chose Robbins because they needed design parameters that encompassed hard rock TBMs, EPBMs, and slurry shields. The EPBM featured eight double and four single backloading 17 inch (432 mm) cutters. The machine was capable of 5,783 kN (1,300,000 lb) of thrust and could generate a torque of 409,457 N-m (302,000 lb-ft) at the cutterhead.

Two face ports at each side of the machine permitted drilling and grouting in difficult conditions. Excavated ground was extracted with a 17 inch (432 mm) diameter invert auger screw. The muck was then conveyed to a mixing chamber to agitate and crush the limestone. The entire excavation system was a closed and pressurized face built to withstand up to 3 bar of hydraulic pressure.

From the mixing chamber, the muck traveled to a slurry pump installed inside the tunnel. The slurry pump transported the muck in a tube to the shaft where it connected with a second pump that brought the muck to the top of the shaft. The slurry pumps directly discharged the cuttings to the surface because the limestone was too porous to form a matrix. Therefore, the sluggish characteristics of the muck made muck transport via screw auger into muck cars too difficult.

Tunnel Excavation

The hybrid EPBM began boring on May 27, 2002. In the early stages of tunnel excavation, the machine operated in usual EPB mode and material was removed with muck cars.

As the machine continued boring, it encountered increasing hydraulic loads of up to 2.5 bar. This anticipated condition was treated with a circular break system that kept the EPBM in place.

However, the high water pressures prevented the excavated material from forming a plug in the screw conveyor. Injection of ground conditioning additives did not improve the situation and water inflow to the tunnel continued. The mucking system was then converted from muck cars to the more efficient slurry system involving slurry pumps.

After the conversion, the EPBM progressed well and broke through on August 22, 2002 only 3 mm (1/8 in) off of target.

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